To address the issue of an ergonomic and intuitive voluntary transition from an autonomous steering mode to manual steering, it has been suggested in US 2013 002416 to provide a vehicle steering system with an autonomous interface steering wheel movable from a first position to a second position and an autonomous driving electronic control unit configured to receive a signal indicating that the autonomous interface steering wheel has been moved from the first position to the second position and initiate change of operation of the vehicle between the manual steering mode and the autonomous steering mode in response to receiving the signal. However, this system does not address the issue of a safe transition from the autonomous steering mode to the manual or driver-controlled steering mode at the initiative of the autonomous driving electronic control unit, e.g. in an emergency situation.
In a somewhat different context, U.S. Pat. No. 6,580,989 discloses a so-called hybrid-type steering system selectively operable in one of three modes: steer-by-wire, electronic power assist steering (EPAS), and manual steering. The steer-by-wire system includes a driver interface system (DIS), a road wheel actuator system (RWAS), and a controller for monitoring and implementing a preferred control strategy. The steering system operates normally in a steer-by-wire mode. Operation in the alternate EPAS mode and manual mode is determined by a controller in response to a malfunction in any part of either the DIS or the RWAS. In each of the EPAS mode and manual mode, the controller causes a clutch mechanism to engage, thus creating a mechanical linkage between the steerable member and the rack and pinion system. In the EPAS mode, one of the road wheel actuator or the reaction torque generator is available to assist in the steering operation. Alternatively, in the manual mode, both the DIS and the RWAS are deactivated and the vehicle is steerable through entirely mechanical means. As the driver is required to hold the steering wheel in all three operating modes, no particular measures have to be taken in the transition between the different steering modes.
Accordingly, there is a need for means to ensure a safe transition from an autonomous steering to a driver-controlled steering in a vehicle when the driver is unaware of the imminence of this transition.